Shrink labels represent a high proportion of labelling applications. High shrink labels are the fastest growing segment in the labelling business due to the trend toward using contoured containers and shrink sleeve labels with 360° graphics for high customer appeal.
Application of heat to a shrink label around a contour container causes the label to shrink preferentially in the direction extending circumferentially around the container and to conform to the outside container shape.
Shrink labels fall into two categories: roll-on-shrink-on (ROSO) labels and sleeve labels. ROSO labels are supplied from a reel, cut into sheets and applied around a container using hot melt to form a seam, with the machine direction (MD) of the film extending circumferentially around the container. ROSO films primarily shrink in the MD direction. ROSO labels generally employ biaxially oriented polypropylene (BOPP) films.
In contrast sleeve labels are supplied from a tube placed around a container, with the transverse direction (TD) of the film extending circumferentially around the container. Sleeve labels primarily shrink in the TD direction.
ROSO labels are preferred over sleeve labels since the sleeve labels are costly as they need to be seamed into a tube in an additional step whereas the ROSO labels are seamed around the container during the labelling step. Additionally application of a ROSO label around a container is a faster process than application of sleeve labels.
Current high shrink sleeve labels are sleeves made of a TD shrink film that is solvent seamed into a folded tube. These high shrink labels provide more than 60% shrinkage and are made of polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene terephthalate glycol (PETG) or oriented polystyrene (OPS). PVC and PET labels are not easily separated from PET bottle flakes using the flotation technique in the recycling process as the films have a density higher than 1 kg/dm3. OPS film requires transportation and storage under controlled conditions due to high natural shrinkage. Natural shrinkage is a shrinkage phenomenon that occurs gradually at a storage temperature in a warehouse, and which causes deformation problems in a roll form.
While ROSO labels offer a cost advantage, the sleeve labels enjoy an advantage in the extent of shrink percentage that can be obtained. Sleeve labels typically shrink up to 60-70% around the circumference of a container whereas commercial ROSO films shrink only up to 20%.
In view of the cost advantage of the ROSO labels, it is desirable to identify a polyolefin based film suitable for ROSO labelling that can shrink around a container to a greater extent than the current BOPP ROSO labels, can shrink in a steam tunnel for high heat efficiency, and has a low natural shrinkage and can be easily separated from PET flakes for recycling. Clarity after shrinkage is another desirable property since the transparent label may be reversely printed to enable consumers to see the printing through the label.
WO2006/071826 discloses multilayer heat shrink film having a core layer comprising a blend of (i) at least one polyterpene and (ii) a syndiotactic polypropylene or a cyclic olefin copolymer (COC) and skin layers comprising one or more polyolefins having an ultimate shrinkage of at least 25% at 135° C. These films suffer from low stability and stiffness.
EP 1632343 discloses a multilayer heat shrinkable film composed of at least three layers comprising skin layers made of resin composition comprising 55 to 95% by mass of cyclic olefin based resin and from 45 to 5% by mass of a linear low-density polyethylene and an intermediate layer composed of a resin composition comprising 95 to 55% by mass of propylene-α-olefin random copolymer and from 5 to 45% by mass of the cyclic olefin based resin. The density and cost of such films are high.
It has now been discovered that by combining a polyolefin core layer with one or two skin layers composed of cyclic olefin copolymer (COC), the resulting film provides a high shrinkage ratio, good operability, optics and stiffness. It has also been discovered that coextruding COC skin layer(s) on a polyolefin core layer, and MD monoaxially orienting the composite film, results in a film easy to tear in TD, which is an advantage for cutting the labels. Finally the multilayer films according to this disclosure are particularly suitable to produce ROSO labels that are easily separated from the PET containers.